Method for fabricating semiconductor device by using etching polymer

ABSTRACT

The present invention discloses a method for fabricating a semiconductor device using an etch-resistant polymer. The method includes a step for the in-situ generation of a polymer layer on the exposed surfaces of a photoresist film pattern, a pad oxide film, and a hard mask layer. This polymer acts as a protective film and prevents photoresist erosion during trench etching processes and improves the etch selectivity. As a result, trench structures can be formed more easily and with improved dimensional control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating asemiconductor device by using an etching polymer and, in particular, toan improved method suitable for a process having a small photoresistmargin during the trench etching process, by generating a polymer on asurface of a photoresist film pattern used as an etching mask. Bygenerating this polymer on the surface of the photoresist before thetrench etching process, and employing the polymer as a protective filmfor preventing photoresist erosion during the etching process, thepresent method improves the etching resistance of the photoresist.

2. Description of the Background Art

When a semiconductor device is fabricated using a method having a designrule below 0.10 μm, the increase in trench depth and reduction in designrule require that the thickness of the photoresist mask is reduced inthe shallow trench isolation (STI) process. Accordingly, the etchingmargin for the photoresist mask becomes excessively small in a trenchetching process. In some cases, the photoresist film will be erodedduring the trench etching process, making it impossible to etch thedesired pattern into the semiconductor substrate while maintaining thedesired degree of dimensional control.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodfor fabricating a semiconductor device by using an etching polymer whichcan improve the etch selectively or etch ratio with respect to aphotoresist, by generating a polymer on the photoresist surface, andemploying this polymer as a protective film for preventing photoresisterosion during the trench etch process, particularly for semiconductordevices fabricated using methods with a design rule below 0.10 μm.

In order to achieve the above-described object of the present invention,a method for fabricating a semiconductor device by using an etchingpolymer, includes the steps of: forming an insulating film having astacked structure comprising a pad oxide film and a hard mask layer on asemiconductor substrate; forming a photoresist film pattern that exposesa device isolation region on the insulating film; etching the insulatingfilm using the photoresist film pattern as an etching mask to expose thesemiconductor substrate; forming a polymer layer on the surfaces of thephotoresist film pattern and the insulating film pattern; form a trenchfor device isolation, by etching the exposed semiconductor substrateusing the polymer layer as an etching mask; and forming a deviceisolation film in the trench.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become better understood with reference tothe accompanying figures. These figures are provided by way ofillustration only and thus should not be understood to limit the scopeof the present invention unnecessarily.

FIGS. 1 through 4 are cross-sectional diagrams illustrating sequentialsteps of a trench formation process of a method for fabricating asemiconductor device by using an etching polymer according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for fabricating a semiconductor device by using an etchingpolymer in accordance with the present invention will now be describedin detail with reference to the accompanying figures.

As illustrated in FIG. 1, a pad oxide film 21 and a hard mask layer 22are formed on a semiconductor substrate 10. Here, the hard mask layer 22may comprise a Si₃N₄ film, SiON film or an oxide film.

A photoresist film pattern 30 is then formed on the hard mask layer 22.The photoresist film pattern 30 is formed in a conventional manner bycoating a photoresist film over the hard mask layer 22 and then exposingthe photoresist to form a device isolation pattern.

As shown in FIG. 2, an insulating film 20 having a stacked structure ofthe hard mask layer 22 and the pad oxide film 21 is then etched usingthe photoresist film pattern 30 as a mask, to expose the surface of thesemiconductor substrate 10.

Referring to FIG. 3, a polymer layer 40 is then formed over theresultant structures formed on the semiconductor substrate 10.

Specifically, the polymer layer 40 is formed by injecting a main gas,preferably Cl₂, HBr, SF₆ or CF₄, into an etching system before etchingthe semiconductor substrate 10 and inducing polymerization of the resistlayer by controlling the plasma parameters within the etching system.The main gas is injected in a flow rate of 10 to 100 SCCM, preferably 30to 70 SCCM. In addition, during the formation of the polymer layer 40,at least one gas selected from the group consisting of O₂, N₂ and aninert gas is also injected into the etching system as an auxiliary gas,thereby enhancing adhesion of the polymer.

The etching system is generally a high density plasma chemical vapordeposition (HDPCVD) system. The plasma parameters for forming thepolymer layer before the etching process are set up so that pressure isbetween 10 and 50 mTorr, the source power is between 600 and 2000 W, andthe bias power is not more than 100 W.

As depicted in FIG. 4, the semiconductor substrate 10 is then etchedusing the polymer layer as a mask, to form trench 50.

In a succeeding process, the polymer layer 40 and the photoresist filmpattern 30 are removed, and a device isolation film (not shown) thatfills trench 50 is formed.

The principle of generating the polymer layer 40 will now be describedin more detail.

When the power is low and pressure is high in the etching system,reactive ion etching (RIE) by ion bombardment decreases and etchingby-products are redeposited on the wafer being etched. That is to say,when the plasma parameters in the etching system are adjusted in orderto form the polymer, carbon and perhaps other organic components fromthe photoresist film pattern 30, silicon from the insulating film 20,and halogen atoms from the main gas are plasma polymerized andredeposited as a polymer layer on the surfaces of the photoresist filmpattern 30 and the insulating film 20. This redeposited polymer layer isvery resistant to plasma etch and thus efficiently protects thephotoresist. In addition, once formed, the polymer layer 40 does nottend to chemically react with plasma consisting of halogen groups, butis physically eroded by high energy ions generated within the plasma.Therefore, etching selectivity between polymer and silicon substrate ishigher than that between photoresist and silicon substrate.

When the polymer layer 40 is formed, at least one gas selected from thegroup consisting of O₂, N₂ and an inert gas is injected into the etchingsystem as an auxiliary gas. The auxiliary gas serves to enhance adhesionof the polymer, thus improving the etch resistance of the polymer layer40.

When the photoresist is subjected to the trench etch process withoutgenerating the polymer layer, the maximum etch depth is about 2500 Å.However, when the photoresist having the polymer layer is subjected tothe trench etch process, the photoresist etching selection ratio isdramatically increased, thereby allowing the maximum etch depth to beincreased to 5000Å.

Moreover, the present invention can also be applied to a trenchcapacitor etching process for forming a trench type capacitor.

As discussed earlier, in accordance with the present invention in thetrench etching process, the use of a thin photoresist film is madepossible by improving the photoresist selection ratio, and a photoresistmargin is increased by forming a deep trench. In addition, using thehard mask layer as an etching mask simplifies the process, therebyimproving productivity.

Using the present method, even on semiconductor devices that are highlyintegrated with design rules below 0.10 μm, and the thickness of thephotoresist film is below 0.30 μm for fine pattern formation processes,conventional etching processes can still be used largely as is, therebysaving the expense of new systems and additional process developmentwork.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiment is notlimited by any of the particular details of the foregoing description,unless otherwise specified, but rather should be construed broadlywithin its spirit and scope as defined in the appended claims.Therefore, all changes and modifications that fall within the metes andbounds of the claims, or equivalences of such metes and bounds aretherefore intended to be embraced by the appended claims.

What is claimed is:
 1. A method for fabricating a semiconductor device using an etching polymer, comprising the steps of: forming an insulating film having a stacked structure comprising a pad oxide film and a hard mask layer on a semiconductor substrate; forming a photoresist film pattern on the insulating film, the photoresist film pattern exposing a predetermined device isolation region on the insulating film; etching the insulating film using the photoresist film pattern as a mask to form an insulating film pattern, the insulating film pattern exposing predetermined regions of the semiconductor substrate; forming a polymer layer on exposed surfaces of the photoresist film pattern, the insulating film pattern, and the semiconductor substrate, wherein the polymer layer is formed by: injecting a main gas into a high density plasma chemical vapor deposition system, the main gas comprising at least one gas selected from a group consisting of Cl₂, HBr, SF₆ and CF₄; injecting an auxiliary gas into the high density plasma chemical vapor deposition system, the auxiliary gas comprising at least one gas selected from a group consisting of O₂, N₂ and an inert gas; and reacting halogen from the main gas with carbon from the photoresist film pattern and silicon from the insulating film to form a polymer; etching the exposed regions of the semiconductor substrate to open a trench for device isolation in the semiconductor substrate; and filling the trench with a device isolation film.
 2. The method according to claim 1, wherein the plasma parameters of the high density plasma chemical vapor deposition system comprise a pressure between 10 and 50 mTorr, a source power between 600 and 2000 W, and a bias power of not more than 100 W.
 3. The method according to claim 1, wherein the main gas is injected at a flow rate of between 10 and 100 SCCM.
 4. The method according to claim 1, wherein the main gas is injected at a flow rate of between 30 and 70 SCCM.
 5. A method for fabricating a semiconductor device comprising the steps of: forming a pad oxide layer on a semiconductor substrate; forming a hard mask layer on the pad oxide layer; forming a photoresist film pattern on the hard mask layer, the photoresist film pattern exposing a portion of the hard mask layer; etching the hard mask layer and the pad oxide layer using the photoresist film pattern as an etch mask to form an insulating film pattern, the insulating film pattern exposing a predetermined region of the semiconductor substrate; forming a polymer layer on exposed surfaces of the photoresist film pattern and the insulating film pattern, without substantially etching the semiconductor substrate, the step of forming the polymer layer further comprising: injecting a main gas into a high density plasma chemical vapor deposition system, the main gas comprising at least one gas selected from a group consisting of Cl₂, HBr, SF₆ and CF₄; injecting an auxiliary gas into the high density plasma chemical vapor deposition system, the auxiliary gas comprising at least one gas selected from a group consisting of O₂, N₂ and an inert gas; and reacting halogen from the main gas with carbon from the photoresist film pattern and silicon from the insulating film to form the polymer while maintaining a basis power of less than 100 W; etching the predetermined region of the semiconductor substrate to form a trench, the trench being characterized by a trench profile; removing the polymer layer, the photoresist film pattern; and filling the trench with a device isolation film, the trench profile remaining substantially unchanged. 